The present invention relates, in general, to power supplies for electrostatic spray guns, and more particularly to a portable, light-weight, compact power pack formed as a replaceable component of an induction spray gun.
Electrostatic spray guns of various types and configurations are well known in the liquid spraying art and have long been used to spray various materials such as paints, insecticides, and the like. Recent improvements of such devices have been in the area of induction charging devices which serve to induce suitable charges on the spray particles produced by conventional spray guns, the improved devices operating at lower voltages and currents than previously was possible with the conventional corona discharge devices. Induction charging spray guns, to which the present invention has particular reference, are disclosed and claimed in copending application Ser. No. 548,958, of James E. Sickles, filed Feb. 11, 1975 and entitled "Improved Electrostatic Spray Coating Apparatus", and in application Ser. No. 634,386, of James E. Sickles, filed Nov. 24, 1975 and entitled "Electrostatic Spray Coating Apparatus", as well as in U.S. Pat. No. 4,073,002 issued on Feb. 7, 1978 James E. Sickles et al, and entitled "Self Adjusting Power Supply for Induction Charging Electrodes", all of which are assigned to the assignee of the present application.
A discussion of induction charging of spray particles may also be found in U.S. Pat. No. 3,698,635, issued on Oct. 17, 1972 to James E. Sickles. As set forth in the foregoing applications and patents, induction type spray guns have numerous advantages over the prior and conventional corona type spray guns. Principal among these advantages is the fact that the induction type spray gun operates at a substantially lower current and voltage level than does a corona device, induction spray guns utilizing voltages in the range of 10-25 kv and currents of about 1 to 5.mu.a, while corona devices typically require voltages of 60 kv and up and currents of 50 to 200.mu.a or more. However, even with such an advantage, a spray gun having exposed electrodes carrying a voltage in the range of 15 kv presents certain handling problems, since a voltage in that range can produce arcing and similar effects. Where the power supply for a spray gun is a separate unit from the gun, it becomes necessary to utilize highly insulated electrical cables safely to conduct the required power to the gun. Such leads are relatively heavy and inflexible, particularly with high voltage corona-type devices, and make it difficult for the operator to handle the gun during a spray coating operation. Although the introduction of induction spray guns has reduced this problem considerably, because of the lower voltage and current requirements of such devices, nevertheless the problem remains, for even these lower voltage levels require substantial insulation for the lead-in cable and within the gun itself.
The power supplies used in the prior art typically are separate units which in order to provide the power levels required, have been extremely heavy, bulky and difficult to move, and have restricted the mobility of the spray gun operator to an area within reach of the high voltage cable leading from the power supply to the spray gun. The immobility of the power supply and the heavily insulated lead-in cable which is required by the prior art devices to provide relative safety in operation not only cause the spray gun to be awkward to handle, but increase the danger to the operator due to the possibility of breakdown of the insulation in the cable or in the power supply and consequent arcing and sparking problems.